The 'new document' crash

[Adrian Page]

Thanks to valgrind, I think I've found the problem with opening a new document 
from a running instance:

It's when it's loading the plugins that contain filters. The KisFilter 
constructor tries to register itself with the filter registry, but because 
the filter already exists, it doesn't get inserted in the map. Since the 
filter passes itself using a KisFilterSP, when that gets destroyed, the 
filter gets destroyed because there are no other references to the filter. So 
the filter gets destroyed inside its own constructor, which is not good.

I don't know what the intentions are for loading single/multiple instances of 
plugins, so I haven't done anything to fix this.

Adrian